BEIJING, China (CNN) -- An executive of the Chinese dairy company Sanlu Group pleaded guilty Wednesday over her role in the contaminated milk scandal that sickened nearly 300,000 infants, state-run media reported.

Tian Wenhua, Sanlu's former board chairwoman and general manager, and three other executives are on trial for producing and selling fake or substandard products, according to Xinhua news agency.

Wenhua, 66, pleaded guilty on the first day of the trial at a court in Shijiazhuang, the capital of northern Hebei Province, Xinhua reported. She told the court that she first received tainted milk complaints from consumers in mid-May -- four months before the issue became widely known -- according to the report.

Wenhua led a working team to investigate the claims, Xinhua reported.

The three other executives are former deputy general managers Wang Yuliang and Hang Zhiqi, and Wu Jusheng, a former executive heading Sanlu's milk division.

Chinese investigators found melamine in nearly 70 milk products from more than 20 companies, according to quality control official Li Changjiang, who was eventually forced to resign.

The Ministry of Health has said the contamination likely caused the deaths of at least six babies. Another 294,000 infants suffered from urinary problems, such as kidney stones.

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The tainted formula came to light in September after babies who were fed milk powder produced by the Sanlu Group, which recently filed for bankruptcy, had developed kidney stones.

Melamine is commonly used in coatings and laminates, wood adhesives, fabric coatings, ceiling tiles and flame retardants. Some Chinese dairy plants added the chemical to milk products so they would appear to have a higher protein level.

Prior to the four Sanlu executives, at least eight people stood trial over charges of producing, adding melamine-laced "protein powder" to milk or selling the tainted milk to Sanlu or other dairies.

Victims of tainted baby formula are expected to be compensated by the 22 Chinese dairy producers that made the milk.

"The enterprises offered to shoulder the compensation liability," the country's Dairy Industry Association said Saturday, according to Xinhua. "By doing so, they hope to earn understanding and forgiveness of the families of the sickened children."

The group said victims will receive a one-off cash payment, but did not provide the amounts, according to Xinhua.

"The money for compensation is in place now and will soon be handed to the people who have custody of the sickened children through various channels," the association said.

No date for the payments was given. The dairies also raised money to cover medical bills for any after-effects suffered as a result of the poisoning, the association said.